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Cretaceous of the Caswell Silver, 1951, pp. 104-118 in: San Juan Basin ( and ), Smith, C. T.; Silver, C.; [eds.], New Mexico Geological Society 2nd Annual Fall Field Conference Guidebook, 163 p.

This is one of many related papers that were included in the 1951 NMGS Fall Field Conference Guidebook.

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Publications of the New Mexico Geological Society, printed and electronic, are protected by the copyright laws of the . No material from our website or printed and electronic publications may be reprinted or redistributed without our permission. Contact us for permission to reprint portions of any of our publications. One printed copy of any materials from our website or our print and electronic publications may be made for individual use without our permission. Teachers and students may make unlimited copies for educational use. Any other use of these materials requires permission. This page is intentionally left blank to maintain order of facing pages. n NEW MEXICO GEOLOGICAL SOCIETY * SECOND FIELD CONFERENCE * SAN JUAN BASIN HI I STRATIGRAPHY OF THE a broadUniform variation has beenestablished which SAN JUAN BASIN is illustratedby Figure I. Sandstonepredominates to J thesouthwest, to thenortheast; marine deposits make ¯ mm CaswellSilver ~ up theentire section to thenortheast whereas deposits ConsultingGeologist to thesouthwest are of intertonguingmarine and contlnentaifacies. I Possiblyfew systems of rocksin westernUnited Sears,Hunt, and Hendricks(1941 , p. 102)reviewed Stateshave been written about more than the Cre- theconcept, in a paperwhich has becomea classic, thatthe deposits under discussion were laid down in a g taceousrocks of theSan JuanBasin. The publications gm listedat theend of thispaper include many papers broadshallow trough that extended across the area in describingthese rocks in everypart of theBasin and lateCretaceous time. The general orientation of the adjoiningareas with a wealthof detailnot possible shorelinewas northwest to southeastand fluctuations [] here.Thispaper will not re-describe all the strati- in theposition of thisshoreline were generally in a II graphicunits. The subject of thispaper is thesequence northeastto southwestdirection. Further, they elaborated of bedsof differinglithology, the lateral variations theconcept first stated by Lee(1915, p. 28)that both the in lithologyof these beds and their relations to the transgressiveandregressive deposits were laid down economicdeposits of ,oil and gasthat have been duringcontinued sinking of thetrough and thatboth II foundand may possiblybe foundin theSan JuanBasin. transgressiveor regressive deposits were a reflection Theworks of previousauthors are drawn upon freely of therate of sinkingin relationto thesupply of HI forthis purpose. If afterreading this paper newcomers material.Figure 2 fromSears, Hunt, and Hendricks havean understandingof the thickness and position of (1941,p. 105)shows the theoretical progression. This | theCretaceous layered rocks and an understandingof wasborne out by the "widespreadoccurrence of trans- thepossible distribution of the contained fluids, the itionzones between shale and overlying regressive ¯ author’spurpose will have been served, sandstoneand by theextent of thicknessand uniformity [] of suchsandstones. With continued subsidence there TheCretaceous of thecentral part of wouldalso be Opportunityfor the development of thick i theSan Juan Basin can be Iogically:divldedinto coal-bearingcoastal-swamp deposits behind and en- ¯ twomajor groups: the older and lowergroup which croachingupon the beachsands as the sandsgrew up- I includesall the sediments deposited while marine conditions ward and seaward. " (Ibid, p. 101).As regression enduredand theupper and younger transitional continuedflood-plain deposits encroached upon the [] whichbridged the transition from marine to wholly near-shareand coastal deposits. At suchrime as the continentalconditions of deposition.If one considers rateof sinkingin thetrough exceeded the supply of theduration of marineCretaceous sedimentation in materialregression ceased and the sea again trans- thecentral part of thebasin as extendingfrom the gressedthe land to the southwest.The upwardsuccession n baseof theDakota to thetop of thePictured of sedimentswas the reverse of thatduring regression U Cliffssandstone, the valuable stratigraphic reference coastaldeposits building upward to thesouthwest over intervalof theolder group is established(See Figure i.) flood-plaindeposits, which were in turnfollowed by R Thisinterval contains most of thecommercial deposits of near-shoresands and marine . oil andgas that have been found in Cretaceousrocks of thebasin at thistime, as wellas mostof theyet un- Age of theFormations. discovereddeposits. This interval lies across theSan Earlyworkers in theBasin were perplexed by the ¯ JuanBasin as a sedimentaryblanket of almostuniform conflictingpaleontologic data relating to theage of [] thickness.Over much of thebasin this interval is made thevarious lithalogic units, It wasnot until the up entirelyof clasticsand is constantin thicknesswith- formationswere mapped on a strictlylithologic basis in a fewhundred feet of 4,700.However, there is a disregardingageconsiderations that the present clear ¯ remarkableuniformity in theVariation in composition stratigraphlcrelationships became evident. As early Ill of thisblanket. In allbut a fewplaces the bottom and as 1915Lee (p. 36-37) pointed out that it wasthe tophorizons consist of sandstonea few hundred feet customthen to assigna sandstoneto theDakota if it [] thick.Between these containing sandstone horizons occurredimmediately below shale known from n ! !

104 I

NEW MEXICO GEOLOGICAL SOCIETY * SECOND FIELD CONFERENCE * SAN JUAN IBASIN ! evidenceto be of Bentonage and thatthe Dakota DakotaSandstone. of onelocality was not the exact time equivalent "TheDakota sandstone," in thewords of Gregoryl I of theDakota of otherlocalities. The transgressive (1917,p. 72)"is highly variable in structure,texture; natureof the’Dakotashown by Lee(1915) and the and composition.It is characterizedmore by a transgressiveandregressive Mesaverde persistentcombination of features than by theper- I describedby Sears,Hunt,andHenrlcks,(1941)and sistenceof any givenbed. The baseis commonlybut ¯ Pike(1947) have established clearly the fact that by no meansuniversally marked by conglomerateand theseformations cut across time lines and cannot be the topis in manyplaces a coarsebrownor gray - definedsolely in termsof age.Figure 3 is a time stonebed but may be a groupof interbeddedsandstones i correlationchart which shows the time relation of andshales or whollysandy shale of yellowor gray thevarious units in theBasin referred to thestandard tones.Coal lenses occur prevailingly in the middle ¯ timescale of theGreat Plains. This figure is in- of theDakota but are found in allpositions from top I herentlyinaccurate as the foregoing discussion has to bottom.The formationis everywherelenticular; shown.:The age of theseformations can onlybe lensesand wedgesof sandstoneof conglomerate, discussedin termsof a specificlocality, of shale,and of coaltens of feetor a fewinches thickoverlap, appear, and disappear along the strike i LowerCretaceous Rocks (?) andvertically in a mostcapricious manner. " The Rocksof earlyCretaceous age havebeen abovegeneral description in the opinion of thisauthor tentativelyidentified by Reeslde (1944) only in the is thebest heretofor written on theDakota sandstone northernpart of theBasin near the town of Dolores of theSan Juan Basin and contains within it cluesto I in MontezumaCounty, , where they have theerratic production history of thisunit. Other a thicknessof approximately100feet.: They consist morecasual observers in theBasin have attempted to of white,medium to fine-grainedsandstone and green systematizethe Dakota.Prevalent are suchexpressions andgray shale. Similar rocks of likethickness appear I as "the secondDakota, .... thethird Dakota. " Such to be locallypresent in northernNew Mexico150 haveno meaningexcept perhaps in veryrestricted milesto theeast at thehead of ArroyoCanjilon in areasyet the error has persisted. A paper by Lyons T. 25 N., R. 4 E. Subsurfaceinformation from (1951)attempts to dividethe Dakota into five members thefew wells presently drilled to thathorizon indicates "onthe basis of lithologyand porosity. " Such members thatthese rocks are generally present in thesubsurface it is purportedcan be correlatedover the entire Basin. throughthe northernhalf of theBasin. The same rocks Theevidence presented by Lyonsfor this division is arenot exposed in thesouthern part of theBasin but ¯ notonly inconclusive but as evaluatedby thiswriter I a thickwhite sandstone dlsconformable with the under- reaffirmsthe description of Gregory. lyingMorrison formation to whichit is usuallyassigned anddlstlnct from the overlyingDakota sandstone may Gregoryreports the thicknessof the Dakotain I yetbe correlatedwith possiblelowerCretaceousrocks Arizonato be 102feet at SteamboatSprings, 245 feet to thenorth. This sandstone is usuallyseparated from at TodiltoPark 54 feetat a pointsix miles ¯ northof theDakota by itscontrasting white color, resulting r i Lohallin theeast face of BlackMesa, 210 feet six fromheavy concentration of white cement, the general milesnorth of MarshPass at thenorth point of Black i absenceof conglomeraticmaterial and an uppersurface Mesa,and 170 feetat CarrizoMountain. In New of tento thirtyfeet of relief.Where rocks classified MexicoRenick (1931, p. 36-39)reports 189 feet as Dakotacontain a middleshale and coalmember and in San MiguelMine Canyon, Sac. 13, T. 19 N., R. I W., I a lowerconglomerate member Reeside (1949) has also 263feet in San MiguelCanyon,Sec.35,T. 20 N.,R. indicateda possible lower Cretaceous age for these ! W.,191 feet six inches in SE I/4Sec. 2, T. 20 N. units.Commercial gas hasbeen reported from the R. I W. northside of SenoritaCanyon. Renick reported rocks|mmedlately below the Dakota at the Stanolind- thesesections in detaileddescriptions. Where these i IgnacloNo. I B wellat Ignacio,Colorado and the sectionswere measured along the east rim of theBasin DoswellNo. I ScottFederal in T. 26 N., R. 6 W. at fivemile intervals they appear to havea threefold Freshwater has been reported from this horizon in the division,consisting of a massivelower bed, sometimes PetroleumProductsInc., No. I SantaFe, in Sac.21, conglomeratic,a shaly middle interval and a massive I T. 21 N., R. 8 W. uppermember. This division does not hold south of the ! ! I 105

NEW MEXICO GEOLOGICAL SOCIETY * SECOND FIELD CONFERENCE * SAN JUAN BASIN

Ojo delEspiritu Santo ranch in T. 16 N., R. I W. variableas itsstratigraphy would indicate. It is wherethe entire consists of massive theprincipal oil horizon in theBasin, at present sandstone.Dane (1948, para. 4) reportsthe Dakota producingin suchfields as Rattlesnake,, 186 feetin Sec.33, T. 27 N.I R. 2 E. Woodetal LindrithPrice, Doswell, Red Mesa,and Table (1948)report a thicknessof 171feet at Chromojust Mesa.Commercial gas is producedfrom it at Barker northof the New Mexico-C01oradollne. Reeslde Dome, Ute DOme, and Kutz Canyon.However, it (1949)reported 250 feet of Dakotain eastern alsoyields potable fresh water, sulfur water, sodic PlataCounty, Colorado, and 200feet plus or minus water,salt water, brackish water, thermal water. in centraland southernSan JuanCounty, New Mexico. Theoccurrence of oiland gasin the Dakotahas been Thicknessesencountered in wells in thecentral part up to thistime about evenly divided between structural of theBasin are about the same as thosereported andstratigraphic traps. Some doubtful occurrences above.Hunt (1936 p. 39) reportsthe Dakotaalong areyet to be classified.The important point about the southernedge of thebasin as attaininga maximum thevariation in fluids is thatthey are irregular in thicknessin theoutcrop of 75 feet"but locally it is differentlenses in thesame well bore. Salt water absent,the overlyingMancos shale resting directly sulfurwater, and oilhave been encountered in uponthe erodedtop of theMorrison... " "East of differentlenses in thewells and it is notuncommon MountTaylor there are threeprominent sandstone~ to find,as at theRattlesnake field that oil is en- in thelower 350 feet of theMancos shale, overlying counteredin lenses,both above and belowother the Dakotasandstone, to eachof whichthe name lensescarrying water. Several deep wells such as TresHermanos sandstone’ has been applied." the Byrd-Frost-HargravesNo. i Sec.4, T. 27 N. Huntthought it probablethat the basal Dakota sand- R. IO V~.~Thomas C. DoswellFederal No. I, Sec. stonewest of MountTaylor is at thehorizon of oneof 10, T. 26 N., R. 6 W., and the Delhi-Magnolia- thesesandstones. The name"Tres Hermanos sandstone" IngwersenNo~ I in Sec.20~ T. 24 N. ,,R.2 W. wasfirst used by Herrickand Johnson (1900, p. 14)and haveencountered sand lenses of low permeability laterused by otherswithout recording a type locality, carryingoil and gas. The restricted nature of the Hunt(op. cit. p.41) used the designations : "sandstone pr0ductionplus the apparent lack of structuralClosure I~ 2~ and 3" wherelocally mappable. In’general on the’surfa,~ewould indicate that such accumulations theterm has fallen into disuse and all of theindividual arein largepart due to the0p-dip pinching out of unitsare collectively referred to as theDakota group, individuallenses. Other fields such as Hogback, (SeeFigure 3). BarkerDome, andPrice have foundsandstones of goodpor0sity and permeability in the same horizon. Coalin the DakotaSandstone Wellswhich have been drilled to the Dakotasandstone Thoughwidely scattered in the Dakotagroup, in theBasin are as yettoo widely scattered to permit coalrarely attains a thickness and continuity to be definingareas of betterporosity~ but some general of commercialimportance. Sears (1925, p~ 24) re- observationsmay be madesubject: ~a futuremodification. portedonly two :places along the Defiance monocline TheDakota sandstone appears to be a freshwater whereit wasfound to reacha thicknessof fourteen aquiferthroughout the structurail.yl shallow Zuni-Gallup inches.Gregory (I.917) reported five feet of coal reentrantof theBasin and immediately adjoining the goodquality containing sulfur six miles north of northflank of theZunl Uplift. S0-called flushing by Lohali,Arizona. Veatch (1911, p. 239-241)describes meteoricwater in structurallydeeper areas is not thecoal near Pinedale, Arizona T. II N. ~ R. 19 E. borneout by presentlyknown occurrences. The lent- as occurringin thevery base of theCretaceous strata icularityof theDakota sandstone is suchthat there andcontaining from two to threefeet of verygood areunllkely to be anylarge specific areas where sub-bituminouscoal. However, there was no distinct porositycan be predicted.Highly porous and per- sandstonepresent resembling the Dakota of otherareas, meablelenses containing oil andgas may be foundin Lyons(1941) reports five feet of coalin theDakota anylocality. the Durangoarea. MancasShale Fluidsin theDakota Sandstone TheMancas ishale is thebody of grayto dark- Thefluid contents of theDakota sandstone are as graycarbonaceous marine shale that overlies the

108 i . . NEW MEXICO. GEOLOGICAL SOCIETY * SECOND FIELD CONFERENCE *SAN JUAN BASIN ! basaltransgressive deposits of theDakota sandstone halfof theBasin. Production is reported from the wherethey are present and elsewhererests upon the sandyGraneros interval in thePrice field in Colorado. pre-Dakotarocks. It intertongueswith sandstone at i successivelylower intervals to thesouthwest and is Greenhorn¯ LimestoneMember almostwholly shale to thenortheast. The greatest The~ Greenhornlimestone member is appliedto a thicknessof Mancosshale in theeastern part of the lowerpart of theMancos shale which is quitelimy in i basinis in westcentral Rio ArribaCounty, New thesouthwest and contains alternating beds of light- Mexicoin the Delhi-lngwersenNo. I in Sac.20, graylimestone and darker gray calcareous shale to T. 24 N., R. 2 W. whereit is 2,185feet thick, it thenortheast. Many workers regard it as a fairly thinsto thesouthwest¯and northeast from that point reliabletime horizon. It is from40 to 60 feetthick i andretains approximately thesame ¯thickness to the and¯ produces a characteristic setof highresistivity northwestto itsoutcrop at Mesaverde.It is about curveson theelectric log. Dane (1948, para. 6) 1800feet thick in easternArchuleta County, Cola- reports,also in thenortheast two thin beds of shaly i ,adoand thinsto 425 feeton the Zunireservationin limestone30 feetbelow the topof bedscontaining the southwest.Gregory (1917, p. 74) reports620 a Granerosfauna which may be mistakenlyincluded feetat LolomaiPoint at thenorth end of BlackMesa, in the Greenhorn.However most workers in the Arizona.As shownby Figure4~ it splitssouthwest- fieldusethe closely spaced light gray, one to two- i wardinto three main tongues on thenorth flank of footthick beds occurring through about a the ZuniUplift. The highesttongu% the Satan 20-footzone as themappable unit in thenorthwest tongue,thins westward and is indistinguishablefrom portionof the Basinand labelit Greenhornwithout ¯ ! the Mesaverdein T. 17 N., R. 15 W. The middle respect:to age. Similar usage is¯applied to thecharac- Mulattotongue extends as farsouthwest as thevicinity terlsticresistivity curves¯mentioned. TheGreenhorn of Gallupwhere it toobecomes inseparable from the fieldunit mentioned does carry a Greenhornfauna Mesaverde.The lowertongue extends¯ far to the everywhere.Shows of alland smallproduction of i sQuthand west and is recognizableas far south as the a light-brownor bright-hued green all havebeen SilverCity area of NewMexico and as far westas the obtained¯from the at widely HopiButtes area of Arizona.It wouldappear entirely scatteredparts of theBasin in-¯Colorado at Red Mesa possibleth0t the Mancosshale has graded completely andthe east flank of BarkerDome¯in La PlataCounty, i to Mesaverdetype sediments at PinedaleArizona. andat Chromoin ArchuletaCounty. Porosity in the limestoneis extremelylow and the best yield reported GranerasShale Member wasfour barrels a dayat Chromo. i Definitellthologic units otherthanthose ¯divided by Mesaverdetongues and locallymappoble have been CarlisleShale Member ¯ recognizedwithin the in theBasin. The The Carlisleshale member can be mappedin Granerosshale equivalent a dark, almost black, evenly rthenorthern part of theBasin. As reportedby Dane I thln-beddedshale unit ranging from 50 to 150feet in it consistsof twoparts a lowerdark shale about 200 thicknessis recognizableover much of the Basin.The feet¯thlckand an upperpart containing "numerous nameis generally¯applied to thatpart of theMancos bedsof harddark-colored platy sandy limestone or shalelying between the Dakotasandstone and the calcareoussandstone. " This upper part is a distinctive i Greenhornlimestone equivalent. This interval is zoneon theoutcrop through all of southernColorado. thickestto thenortheast and thins to thesouth and Dane~1948 para. 10) reports a thicknessfor the west.In southernNew Mexico in thevicinity of the Carlisleof 600feet in thevicinity of El Vadofrom i townof Truthor Consequencesthere is no shaleinterval whenceit thinsto the northto 500feet on the Monero betweenthe Dakotaand the Greenhornlimestone and Dome.The upper part often weathers a silverygray theyare in contact.This would indicate that far to on theoutcrop and makes a distinctcolor band where thesouth the Dakota sandstone is possiblyof Graneros theMancos is wellexposed. This unit is themost i age.Locally even as farnorth as thecentral part of importantproducing interval of theMancos shale. theBasin the interval is occupiedby Straysands occur in it in allparts of theBasin, sandstoneswhich are groupedwith the Dakotasandstone becomingmore common to the southwest.The "stray i asmentionedabove. Thln bedsof bentoniteup to six sandstone"of Sears,Hunt and Hendricks(1941, p. inchesthick occur in theGraneros shale in thenorthern 113)occurs in thisinterval. Small sand lenses ¯ in ! ! i I09

I NEW MEXICO GEOLOGICAL SOCIETY * SECOND FIELD CONFERENCE * SAN JUAN BASIN

I thisinterval produce the shallowproduction at Chromo Manywells scattered over the Basinand abandoned Coloradoand it is theinterval containing the stray in the Mancosshale before reaching the Dakota producingsand at theThomas Doswell well in Sec. sandstonehave reported making small amounts of I 9, T. 26 N.,R. 6 W. Thisis alsothe interval split gas.Several of themare usedas domesticsources by the’Gallupsandstone tongue of the Mesaverdeto of fuel. thesouthwest which further north has been called theTocito sand stone. Pike (1947, p. 29) showed MesaverdeGroup I thatthe Gallupsandstone member Dilco coal The-Mesaverdegroup is the nameapplied to the memberand Daltonsandstone member are essentially regressiveand transgressive wedges of sandstonewhich equivalentto the Tocitoand he recommendedthat the intertonguewith the Mancos and to the i latterterm be dropped.However, production has been southwest.The termformation is generallyapplied establishedwithin several sandstone bodies in this to portionsof theBasin where individual mappable zoneand thename continues to be employedin the unitsare not distinguished. Thisapplies both in the allindustry. With the important Doswell all discovery northeastwhere the Mesaverdeis recognizedas one I in thishorizon in T. 26 N.,R. 6 W. it appearsthat overallsandstone wedge and in the westwhere sand- theterm will become more firmly established than ever stone,shale, and coal are extremely irregularly inter- andthat the only recourse is to giveway to itsusage bedded.Group was the orlg~nalterm applied by I as a zoneterm recognizingthatproductionin the Holmes(1877,p. 244)when he namedthe unitfrom "Tocito"in differentfields or evenin thesame field the localityat MesaVerde and recognized three format- is notnecessarily from the same continuous sandstone ations.Collier (1919, p. 296)renamed the subdivisions lense, of Holmes,the , the Menefee I formation,and the PointLookout sandstone. The U. S. " NiobraraShale Member and UpperShale Member GeologicalSurvey has followedthe practice of re- TheNiobrara calcareous shale member is sep- ferringto theMesaverde as a groupat thetype I oratedwith difficulty from the overlying Upper shale localityand its vicinity and as a formationelsewhere. memberof the Mancos.Dane (1948) has distinguished In additionthe Surveycarr.led the nameMesaverde themin hismap of partof theeastern Basin but they forcoal-bearing formations in the middle part of the cannotbe distinguishedeither in wellcuttings or in UpperCretaceous series as tar awayas . I theoutcrop without the presence of .Their usefulnessas units would appear to be highlyrestricted TheMesaverde of the Basincan be conveniently if notnegligible. In that area Dane (1948, para. II) dividedinto two parts for discussion; (1)the original gives250 to 350feet for the Niobrara and 500 to 700 groupof Holmesand its extension north and east, and I feetfor the Uppershale member of theMancos. (2)all the regressive and transgressive sandstone units thattongue to the Mancosshale below theorlginal Fluidsin the MancasShale groupof Holmes.The baseof the Mesaverdemay I The Mancosshale is productiveof alland gasin theoreticallyfall as lowas thetopof theDakota severalparts of the SanJuan Basin. All occurrences sandstoneor thepre-Dakota erosion surface in reportedhave been small except for the production localitiesfar to thesouth and west. Inasmuch as the ! reportedin thePrice field in Colorado.In this Mesaverdeis eroslonallytruncated to thesouth and I fieldwells were reported to hovemade a potential weston theflanks of theZuni and Defiance Uplifts of severalhundred barrels a dayin theMantas shale thediscussion which immediately follows will be abovethe Dakotasandstone. At Chromo,eight miles confinedto thefive members into which part (2) to thewest of thePrice field and four miles north of hasbeen subdivided in the southern part of theBasin. I the New Mexicostate line, more than a dozenwells atecurrently productive from sandy lenses in the The GallupSandstone Member Carlisleshale and from fractures. Wells there have Stray([. e., unnamed) sandstones intertongue with I hadan initialpotential as highas 200barrels per day the lowerpart of theMancos shale betweenitsbase buthave declined within a fewdays to 5-:10barrels per andthe base of theMesaverde but the first persistent day.Some of these"shale" wells have made an average regressivesandstone which has beenmapped over a of fivebarrels a dayfor more than three years at depths largearea is calledthe . In the I 0~ lessthan 600 feet. Gallup-Zunibasin the Gallup sandstone consists of ! : ! III ! NEW MEXICO GEOLOGICAL SOCIETY * SECOND FIELD CONFERENCE * SAN JUAN BASIN U

n threepersistent, massive sandstones and interbedded BartlettBarren Member shaleand coal 180 to 250feet thick. I.The lower one In workingwith the Mesaverde formation of of thesesands splTts to theeast and northeast, being westernand southwestern parts of theBasin, Sears n recognizedwest of MountTaylor as two sandstone" (1925p. 16-17)apparently found it difficult tongues’in the upper part of themain body of the separatethe flood-plain deposits from the coastal Mancossl~ale. The upper two sandstonesof the Gallup depositsalthough he clearlyfelt such a distinctlon m convergeto theeast and northeast, pinching out the existed.In mapping,it is apparentthat the sediments ¯ interveningcoaF andshale and gradually replace the immediatelyoverlying the off-shore and beach deposits i overlyingDilco coal member. Where it~appears on containmore numerous and thickercoal beds than the thesurface in northwesternSan JuanCounty it is contiguousflood-plain deposits and that they do not [] knownas the"Tocito" sandstone. As is thecase with exhibitthe scour and fill relationships to as marked mostregresslvesandstones in thearea, the base is a degree.Since the intertongulngprevents any oftentransitional to Mancos shale, sharpseparation, Sears arbitrarily divided the two on thebasis of thenumber and thickness of thecon- ¯ Dilco Member :: tainedcoal beds. Those sediments containing com- e Thismember is 240-300feet thick in the Gallup- merclalcoal beds over fourteen inches thick were mapped ZuniBasin and is .graduallyreplaced northeastward by as coalmembers and the contiguoussediments generally [] sandstoneand shale.It containsmany of the valuable containingcoal beds of lesserthickness were termed !1 coalbeds in thewestern part of theBasin and gets its the barrenmembers. namefrom the village of Dilco(Direct Line Coal Company).It is uniquein the San JuanBasinin that TheBartlett barren member contains beds lltho- ¯ overa largearea it is.directlyoverlain by theMulatto logicallysimilar to thebeds of theDilco coal member. tongueof the.Mancos shale. Together with the Gallup In theGallup-Zuni Basin this interval is 330to 400 sandstoneit is theonly regressive unit in theBasin feetthick and is separatedby Sears(1925 p. 17)from ! whichdoes not have a continuouslittoral sandstone the Dilcocoal member. Actually as discussedabove ¯mm interveningbetween it and theoverlying marine shale theseparation is purely arbitrary; the Bartlett member andtherefore it is similarto thesedimentary sequence is madeup of theflood-plaln deposits which increasingly of theBook Cliffs of .In thisrespect it: is. the domlnatethe Mesaverde to thesouthwest. In all prob- ¯ onlyregressive sequence of the Mesaverdeknownto abilitythis unit converges to thesouthwest with the the.authorwhich does not combine with a transgressive Allisonbarren member as the overlyingGibson coal sandstoneto forma wedge.ofdual nature, as discussed memberwedges to a thinedge. by Spieker(1949, p. 66).This could result from i morerapid shoreward shift of strandlTneorsudden rise GibsonCoal Member in sealevel. In the Gallup-Zuniarea the Gibsoncoal member consistsof 150-175feet of ,irregular sandstone i DaltonSandstone Member ... andcoal which thicken northeast until at thenorth TheDalton sandstone member in its extremesouth- end of the Nutriamonocline in T. 17 N., R. 17 W. II westernposition is themissing littoral sandstone enclosing it is 350feet thick. Just northeastward from this theMulatto tongue of theMancos shale (see Figure 3). locationit splitsinto two tongues enclosing the Hosta ¯ It doesnot extend into the Gallup-Zuni basin. It sandstonemember of the Mesaverde.The lowertongue [] splitsinto two tongues northeastward, thelower tongue is thecoaliferous coastal lagoon and swamp deposit ~ interveningbetween the Mulattotongue of the Mancos betweenthe convergingwedge of the underlyingre i shaleand the Dilco coal member for a few milesbefore gresslveDalton sandstone member and theoverlying ¯ lensingout. The uppersandstone tongue of the main transgressivelower Hosta sandstone member. The u bodyof theDalton is theregressive sandstone lying uppertongue is thecoastal swamp deposit lying above abovethe Mulattotongue of the tv~ncosshale. Where theupper Hosta.sandstone member. In its furtherex- ¯ theDalton sandstone is .notsplit by shalein T. 16 N., tensioneast and north it is thelower part of theMenefee R. 16 W. it is 180feet thick but eastward Tt splitsinto formationin the areawhere the UpperHosta sandstone an upperUnit above, the Mulatto tongue 96 feetthick and bearsthe designation of the sandstone. a lowerunit included between two tongues:ofshale ¯ 72 feetthick. ( Sears,et al,1941 ). ! ! ’112. I NEW MEXICO GEOLOGICAL SOCIETY¯ * SECOND FIELD CONFERENCE :*..SAN JUAN BASIN .. . .

! AllisonBarren Member a massivebed of medium-grainedsandstone 100 to 300 feet.thick, ¯¯extensive in the subsurface and¯continuous The Allisonbarren member makes up the upper to thenortheast to the. vicinity of theStanolind-Rosa I. . partof theMesaverde in thesouthwestern part of theBasin. It wedgesto thenorth and east where it UnitNo. I wellin Sec.II, T. 31 N., R. 6 W. where it thinnedand became indistinguishable fromthe thin formstogether with the Gibsoncoal member the i Menefeeformation of thecentral part of theBasin. sandstonesin thelower part of theMesaverde formation. it thickensrapidly to thesouthwest near Gallup where MenefeeFormation and the Alllson-GibsonMember its topis eroded.In Sec.32, T. 16 N.,R. 18 W. a Withthe establishment of the equivalenceof the I thicknessof 800 feet is reportedby Sears(1925,: p. 18) PointLookout sandstone and the UpperHostasandstone fromdrill-hole information, memberas one continuousregressive sandstone horizon, it waslogical to recognizethat the overlying coastal LowerHosta Sandstone : swampdeposits were also continuous. Silver (1950, I Thelower Hosta sandstone is the lowerbed of a p. II0)pointed out that such deposits were an over-all :thicksandstone 200 feet in thicknesswhichlies be- wedgeto thenortheast within the convergingregressive tweenthe lowerand upperGibson coal members along PointLookout and CliffHouse sandstones and that the southernboundary of theNavajo Indian¯reservatlon thesedeposits finally merge into the over-all sandy i in T. 17 N.,ranges II to 15 W. The Satantongue of. Mesaverdeformation (see figure I). ¯ theMancos shale splits this sandstone into an upper and lowerunit. The LowerHosta sandstone converges At the typeiocallty¯at Mesa Verde the Menefee withthe UpperHosta sandstone in approximatelySec. consistsof 400feet of coal,.shale, and.sandstone and I 2 T. 17 N., R. 15 W. wherethe Satantongue wedges it thickenssouthward to theGallup area where it is " " to a thinedge. It is thetransgressive sandstone under- subdividedinto the members¯alreadydescribed. Pike lyingthe Satan tongue and in turn~s underlainby the. (1947,p’. 49) reports .the Menefee as 812feet in Sec. i LowerGibson coal member. The lowerHosta sandstone 17, T. 29 N., R. 16 W. a pointapproximately 35 miles is about100 feet thick through most of itsextent but . southof thetype locality and 90 milesnorth of the gradesto sandyshale to theeast in T. 16 N.,R. I W. Galluparea. In thelatter area the tap oF elqulvalent on theOjo del Espiritu Santo Grant. sedimentsis erosionallytruncated and Sears ¯(1925 p. I 16)reports an incompletethickness of approximately PointLookout Sandstone and 1600feet. While the Menefee deposits are in large UpperHosta Sandstone Member partcontinental in origln they are not entirely so and I In introducingthe subject of theMesaverde it mustbe emphasizedthat evenfarto thewest in sedimentsof theBasin, a twofold division of the BlackMesa some units containing marine fossils are entiresequence was proposed, followed by a dis- present.It wouldappear that during transgressions of cussionof part2 in termsof theindividual units. A thesea far to thewest local inundations flooded well discussionof part I follows, backupon the coastal plains deposits and left a marine invertebratefossil record intercalated in otherwise To manyin theoil industry of theBasin the continentaltype deposits. The continentaldeposits Mesaverdeis the PointLookout sandstone, ¯ Menefee arecharacterized by thick lenses¯of sandstone, coal formationand CliffHouse sandstone of thenorthern andshale in intricatescour-and-fill relationship as partof theBasin. This is a naturalresult of subsurface contrastedto the more regular bedding of thecoastal developmentit, areas close to wherethese units have deposits. i beenwell defined on thesurface. Correlation of these unitswith similar units termed Upper Hosta sandstone member,Allison-Gibson member and Chacrasandstone CliffHouse Sandstone and the ChacraSandstone memberbecame evident when Pike (1943, p. 37) Member. i establishedthe fact that the Upper Hosta sandstone of TheCliff House sandstone of the¯northand the thesouthern part of theBasin was traceable into the Chacrasandstone and La Ventanasandstone of the Paint Lookoutsandstone as one continuousUnit. Zapp southare deposits of I~hetransgressive transition zone I (1949,para. 9) distinguishedan upper massive sandstone betweenthe marine Lewis shale and thelargely non- memberof thePoint Lookout sandstone on the surface marineMenefee formation. These transgressive de- in theDurango area. Silver (1950, p. II.0)showed that positsdiffer from the regressive sandstones in that i .theupper part of thisregressive sandstone consisted of theyare not continuous sand bodies but rather a con-

!

"" 113 Ii NEW MEXICO GEOLOGICAL SOCIETY * SECOND FIELD CONFERENCE * SAN JUANBASIN

: " " " " I m tinuouszone of sand¯ lenseswhich tongue deeply to wouldindicate that there will not be an Oilring boththe Lewisshaleand the Menefeeformation, aroundthe gas withinthe mE Lensing0flsands in thistransition zone is wellknown to thewest. Information to the south and east is i in boththe surface and subsurface.Lenses of sand- insufficientto support a similar conclusion there; it stoneappear to be gradatlonalat any horizonnorth- is possiblethat the petroliferous accumulation in the eastwardinto marine shale of theLewis f0rrnatlon PointLookout sandstone did not extend to thepresent ¯ and¯var gradationallable southwestward into the highly outcropin thatdirection. Local lenses within the shaleand sandstone of the Menefeeformation. Be- Menefeezonehave encountered sandstones conta|ning causeof theirrestricted extent the lenses of this oil.A corecontaining four feet of fullySaturated oll transgressivetransitlonzoneapparentlydo not¯rise sandwas "pulled" from the Menefeeof the Ston01ine- I stratigraphically.Thezone rises stratigraphically ¯¯ElliotNo. I B in Sac.14, T. 29 N., R. 9 W. Shows II butnot theindividual lenses. They differ markedly of oiland production of a fewbarrels of o~1a dayare fr0mthe Point Lookout sandstone in thatsuch lenses indicatedin wellsdrilled in theMesaverde in T. 18 ¯ ¯ formseparate local units imbricated upward to the ~N,, R. 3 W., Red Mountainand SevenLakes and ii southwest-- suchas theLa:Ventana sandstone :scatteredareas in thesouthwest partof the Basin. and:the Chacrasandstone, whereas the regressive ¯Becauseof theirdiscontinuous nature it canbe anti- m sandstonesrise stratigraphlcally as continuous blanket : cipatedthat the sandstone lenses not yet exposed by sandstoneswhose lower ¯margins intertongue with shale, erosionthat occur within the transgressive sandstone I i zoneswill contain oil and gas accumulations.Where Coalin the Mesaverde suchsubsurface lenses have the extent of 5 X 10 miles ¯ Thecoal beds of theMesaverde are the principal and larger,similar¯t0 ka Ventonasandstone on¯the I coaldeposits of :theSan Juan River region. Coal is surface,¯ large accurriulations arepossible. foundthroughout the Mesaverde but the thickestand mostcontinuous beds have been found principally in Thelower Mesaverde is partof thewedge belt ¯ thecoastal swamp deposits immediately above re- of porositypinching out to thenortheast. Silver gressivemarine sandstones and immediatelybelow (1951)pointed out that its occurrence in the subsurface transgressivemarine sandstones with which they are is mostlyover the south half of theBasin, an 0reain oftenin directcontoct~ In thesubsurface of the whichfew wellshave been drilled. The occurrence centralpart of theBasin the larger coal beds Which of saltwater and oil shows in thefew wells drilled yielda distinctiveresistivity "kick" on theelectric to thishorizon is highlyencouraging. Buried, sealed logare found close to thetop and the base of the sandstonelenses in thesubsurface, such as the"stray Menefeeformation. Because of thediffering strati- sandstone"of Sears, Hunt and Hendricks (1941, p:. tl3) graphicrelationship between the regressiv e andtrans- andthe La Ventanasandstone are to be anticipated; gross|re sandst0nes the more continuous coal beds ..... lieabove regressive sandstones. The LewisShale : TheLewis shale, a thickbody of sandy¯gray marine Fluids~in the Mesaverde shalelying between the Mesaverdeand thePictured TheMesaverde contains within it the sedimentary Cliffssandstone is a wedge~-shapedbody that thins to depositsformed: near the demarcationbetween marine thesouthwest and thickens to thenortheast. The thick- andnon-marine environments and it is ¯onlynatural nessof theLewis shale from north to southon thewest to anticipatefluids reflecting both. Fresh water, slideof theBasin is 1700feet at¯the type locality in brackishwater, salt water, gas, and oilhave been Colorado,1,100 feet at NavajoSprings, 475 feet on encounteredin well bores in thiszone. Silver (1950, theSan JuanRiver and 76 feetat CoalCreek (Reeside, p. 109)emphasized that the Mesaverdegroup is an 1924,p- 17).:It is thickestnorth of PagosaSprings ~n :over-allwedge of porosityand permeability :between ArchuletaCounty, Colorado where it is 2,580feet. the ConvergingLewis and Mancosshale formations Sandyzones are commonin the Lewisshale and one (Fig.4) andthat :large accumulations of gas are of themhas produced gas and distillate ¯ in theUnion presentin thenortheast end of somesandstone lenses. O11 and MiningCompany No. 2 Pinewell in Sac.8, Thelow permeab[lities encountered in¯the gas reservoirs T. 29 N., R. 9 W. plusthe lack of freeoil in thesehorizons where well boreshave encountered the gas and waterContact

:. :..

114~.

¯ " " m m NEW MEXICO GEOLOGICAL SOCIETY ~¯SECOND FIELD¯¯CONFERENCE *SAN JUAN BASIN ¯ . .:.!¯ . .. i . .. PicturedCliffs Sandstone County.The three members also thin in the same sIn the1950 Guidebook (Silver, p. 112)appear di.rection,the lower shale member from 550 feet to thefollowing description: "In additionto beingan zero,the middleFarmlngton sandstone member from importantproducing horizon, the Pictured Cliffs is 480to Zerofeet~ the uppershaJe member from 675 feet themostperslstent andvaluable subsurface stratlgraphic to zero. datumin the Basin.Many:workers have noted its close : : I resemblancein lithology and generalappearance to the Coalin theFruitland Formation : PointLookout sandstone (Zapp, Sheet I). It is the TheFrultland formation is oneof theimportant uppermostwholly marine lithologic unit in thebasin and coalhorizons in thenorthern and central parts of the it recordsthe final withdrawal of the Cretaceous sea ¯Basin.Most of thecoal beds¯occur in the ¯lower halt I in thearea. Where it is foundit is mediumto fine of theformation. In the subsurface of the central part grainedand at anystratigraphic horizon it is grodationalof theBasin coal beds immediately above the Pictured northeastwardinto Lewis shale. It rangesfrom 501 to Cliffs¯. sandstone are important stratigraphlc ¯markers i 400feet in thicknessand crops out on thenorth, west Coalin thishorizon is usuallyfive to 14 feetthick andsouth sides of thebasin. It is notablyabsent on but in the HauckNo. I in Sec.I, T. 29 N., R. 10 theeast side. Its top over large ¯ areasis recognized W. morethan 80 feetof coalbedsseparated by thin as virtuallya stratigraphic plane and it is usedas such shalebreaks was reported. This is very¯similar to the I inFigure I. " 80 feetof coalreported for the "Carbonero Bed" near Duran9o(Zapp, 1949). Silver(1950, p. 112)shows the separation of the PicturedCliffs sandstone into an upperand lower Fluidsin theFruitland and Kirtland Formations I stratigraphic¯ unit (Figure I). The lower or southwestern Commercialgas has beenproduced~from the lobeof thePictured Cliffs is an important¯ gashorizon Fruiflandformation and commercial oil andgas from in theBasin. Gas is widelydistributed in the Pictured the FarmingtonSandstone member of the Kirtland i Cliffssandstone over ¯morethan 1,500,000 acres and formation.The Fruitland production consists of two appearsto have’accumulatedin the northeastend¯of types.Segregated sand lenses in the Blancoarea thesouthwestern lobe at a ¯timewhen this unit was haveishown gas in whatappears to be a stratigraphlc inclinedto thewest. Water¯ is apparentlyencroaching trap.Wells have also tested gas i n thebeds which are I fromthe outcrop in someareasat the present time and called"Fruitland" in the Ignacio::area, Colorado. The thearea of gaswill apparently be limitedonly by the latteroccurrence appears¯to be a structuralaccumulation extentof waterinvasion. No freeell has as yet been in a locallytransgressive tongue of thePictured Cliffs foundin " thePictured Cliffs sandstone and none is formation.¯ Sincethe Pictured Cliffs sandstone occurs I indicatedfor thesouthwestern lobe. However, there twicein the¯wellbores separatedby a regressive is no apparentreason why accumulations could not be tongueof coal--bearingbeds similar to thelog of the: present in thenortheast lobe where structural conditions RosaUnit No. I well¯(Figure I), the term "Fruitland" i arefavorable, is erroneouslyapplied to the¯uppergas horizon. Else- wherein the Baslnsaltwater occurs in lensesof the ..... Fruitlandand Kirtland Formations Fruitlandformation and brackish water in the¯coal TheFruitland ¯formation is the name applied to horizons. : I the 200-300feet of coal-bearingcoastal swamp and flood-plalndeposits which accumulated behind and TheFarmington sandstone member is::largely¯ a abovethe near-shore sands of thePictured Cliffs ¯ : concentrationof sand lenses in themiddle portion Of i sandstoneas it retreatedto thenortheast. After the theKirtland formation. Individual lenses have pro- retreat-ofthe Cretaceous seas from the area, a late ducedsalt water, oil and gas.Commercial gas was Cretaceousbasin of deposition,which has beencalled producedfrom this zone near Aztec andBIoomfield ~ theKirtland Basin (Silver, 1950, p. 112),de~(eloped andsmall commercial ell wells with an :i’nitialproduc - I in thewestern half of thepresent San Juan Basin. In tionof 25 barrelsa dayare reported from the Oswell it accumulatedthe , with its three- fieldby Bates(1942, p. 115).Production of 57°gravity foldlithologic dlvlsions. The Kirtland formation is a ellis reportedfrom different levels in offsetwells. A I wedge-shapedmass of sedimentwhich thins from a wellin the Blan¢ofield tested 4Obarrels a day ~oma maximumof 1700 feeton the Colorado-NewMexico sandstonelens in thiszone butwas perforated into linein T.114W. to a thinedge in centralRio Arriba .. I !

I i. i :. 115 .,.

! , NEW MEXICO GEOLOGICAL SOCIETY ~ SECOND FIELD CONFERENCE * SAN JUAN BASIN I

¯¯ : i water.¯ Smallcommercial oil productionfrom this formations.Dane (1946, para. 7)and Wood et zonewas also reported in theIsrael we!! in the (1948,para. 21) haveheld that~the Animas intertangues ¯ F ulcherBasin area. The largest field as yetdeveloped in thenortheast part of theBasin with beds as oldas inI theFarmlngton sandstone was the Bloomfield pool the Lewisshale. Others (Reeslde 1924, p. 48-49) whichhad a totalof thirtyproducingwells out of : andSilver (1950, p. 121)hold that a hiatusexists some60 drilled.Bates (op. cir., p. 96) concluded the baseof theAnimas. While deposition of sediments I that¯ the accumulation is due to shale-sealedlenses mayhave ¯been more or lesscontinuous in theKirtland II as neithersurface or subs~facedata indicate any Basinduring latest Cretaceous time, these beds lap structuralclosure, uponthe east flank of theKirtland Basin and later [] reworkinginto lower beds of the]Animas has obscured I McDermottFormation : the¯hlatuswhich could have followed the deposition TheMcDermott Formation:: lies in thewestern of theKirtland shale. The relationship of the Animas ¯ halfof theBasin as a thinwedge on topof theKirt- formation,as g~venby Dane,is oneof progressive ¯ landshale. Its greatest thickness is 300feet and it overlapto thesouth in whichsuccessively higher and i thinsto thesouth and east and becomes indistinguish- youngerbeds appear at i!tsbase. Such a relationship ablefrom the Kirtland shale in thesubsurface in the is notin conflictunless accompanied by intertongulng. i centralpart of theBasin. In itsnorthern extent it I consistsof lenticularsandstones~ , and con- Coaloccurs in scatteredseams in thebeds above glomeratescontaining much: andes¯tic debris and : theFruitland formation, but none appears to be thick usuallyit is in partof purplecolor. It gradesto enoughor to havecontinuity sufficient to be of ¯ purplestreaked shale away ¯from its thickest occurrence commercialimportanc e. Scatteredshows of gas alongthe C01orado-NewMexico boundary in R. II W. havebeen reported from shallow wells in the Animas It appearslocally Unconformable to the beds above butprospects for commercialproduction do not and¯below, ¯ appearfavorable. Potable fresh water and sulfurous I "blackwater" poisonous to stockoccur in bothwells [] ale AlamoSandstone andsprings in theAnlmas beds in thecentral part The ale Alamosandstone is an approximately: of theBasin. ¯ 200-foot:thick conglomeratic:: sandstone containing I occasionallenses of shale.It appearsto be restricted Conclusion to thewestern and southern¯ portions of theBasin where Thestratigraphy reviewed in thispaper has it overliesthe McDermott formation or restsdirectly necessarilyemphasized the dlscontlr~uous iithology ¯ uponthe Kirtland shale. Several ha~e of thevarious units. Variations of permeability beennoted above, below and withinthe ale Alamo havebeen demonstrated in these :units in theso- sandstonebut these have ¯been interpreted by Dane calledgas areas (Silver, 1950). The known fields am (1946,para. 7) as notbeing significant either as time andnumerous shows of elland gas indicate that these I lapsesoras intervalsnf erosion.Others have held unitsare petrollferous. It is theauthor’s belief (Silver~1950 p. 112)that such unconform:1ties become thata largepart of theoriginal fluids developed in moreimportant as timebreaks in areasaway from the theCretaceous strata¯are still confined to theBasin ¯ KirtlandBasin:. by theaforesaid lentlcul:arity. Aside from structural accumulationsstratigraphic traps containing minor and Anlmasand Naclmlent0Formations majoraccumulations are veryprobable. The Animasformation consists of some2,000 feet " ¯ c~fgreenish and tan andesltlc sandstones and shales II lyingin thenorthern half of theBasin. Its lower part containsthe latest Cretaceous deposits in theBasin ¯ andits upper part is gradationalinto the Nacimiento I formationof thesouthern¯part of the Basin which containsbeds of Puercanand Torrejonlanage. A differenceof opinion exists as to therelation between the ¯ theAnimas ¯formation and the underlying Cretaceous ! i

I m . J NEW MEXICO GEOLOGICALSOCIETY * SECOND FIELD CONFERENCE * SAN JUAN!BASIN ! SelectedReferences

I Bates,R. L. (1942)The oil andgas resourcesof New Mexico:N. Mes.Bur. of Minesand Min.Res. Bull. 18.

Campbell,M. R. and Gregory,H. E. (1909)The BlackMesa coal field, Arizona. U. S. Geol.Survey Bull. I 491,pp. 229-238.

CollierA. J., (1919)Coal south of Mancos¯Montezuma County, Colorado, U. S. Geol.Survey, Bull. 691.

I Dane,C. H. (1936)Geology and fuelresources of the southernpart of the San JuanBasin, New Mexico. Part 3: The La Ventana-ChacraMesa coal field: U. S. Geol.Survey Bull. 860-C. I DaneC. H. (1946)Stratigraphic relations of EocenePaleocene and latestCretaceous formations of eastern sideof San JuanBasin, New Mexico:U. S. Geol.Survey Oil and Gas Invest.Prelim. Chart 24.

Dane C. H. (1948)Geologic map of eastern:SanJuan Basin,Rio ArribaCounty¯ New Mexico:U. S. Geol. I SurveyOil and Gas Invest.Prelim. Map 78.

Gregory,H. E. (1917)Geology of the Navajocountry. A reconnaissanceof parts of Arizona,New Mexico¯ I and Utah U. S~ Geol.Survey. Prof. Paper 93. Herrick,C. L. and JohnsonD. W. (1900)The geologyof the Aibuquerquesheet,New MexicoUniv. Hadley i Lab.Bull., Vol. 2 pt.I¯ p. 14. Holmes,W. H. (1877)Report on the San Juandistrict, U- S- Geol.Geog. Surv. Terr., 9th Ann.Rept., 237-276.

I Hunt,C. B. (1936)Geology and FuelResources of the Southernpart of the San JuahBasin New Mexico Part2: The MountTaylor Coal Field: U. S. Geol~Survey Bull. 860-B. I Lyons,Thomas R. (!951)Sedimentary Petrology of the Dakotasandstone in the San JuanBasin of New Mexico and Colorado.Univ. of New MexicoMaster’sThesisUn 30 ly 378.789.

Pike¯W. S., Jr. (1947)Intertonguing marine and nonmarlneUpper Cretaceous deposits of New Mexico,Arizona I and southwesternColorado: Geol. Sac. America, Memoir 24.

Reeside,J. B.,Jr. (1924) Upper Cretaceous and Tertiary formations of thewestern part of theSan JuanBasin I Coloradoand New Mexico:U. S. Geol.Survey Prof. Paper’134. Reeside¯J. B. Jr. (1944)Maps showing thickness and general character of theCretaceous deposits in thewestern i interiorof the UnitedStates, U. S. Geol.Survey Oil & GasInvestigations, Preliminary Map 10. Renick,B. C. (1931)Geology and ground-waterresources of westernSandoval County, New Mexico:U.S. Geol. SurveyWater-Supply Paper 620. i Sears,J. D. (1934)Geology and fuel resources of thesouthern part of the SanJuan Basin, New Mexico:Part The coalfield from Gallup eastward toward Mount Taylor: U. S. Geol.Survey Bull. 860-A. I Sears,J. D. Hunt,C. B. and Hendricks,T. A. (1941)Transgressive and regressiveCretaceous deposits southernSan JuanBasin New Mexico:U. S. Geol.Survey Prof. Paper 193-F. I I i 117 NEW MEXtCOGEOLOGICAL SOCIETY * ¯SECOND ¯FIELD CONFERENCE * SAN JUAN BASIN

" ": I SelectedReferences, continued:

Silver,Caswell:(1950) Theoccurrence of:gas in theCretaceous rocks of the San JuanBasin, New Mexico GeologiCalSoCiety Guidebook of the San Juan Basin,New Mexicoand Colorado,pp. 109-123 i

Silver,Caswell (1951) Stratigraphic oll andgas possibilities in the San Juan Basin, New Mexico and Colorado. AAPGBull. May 1951,pp. 1105-1106.Abstract o1: paperdelivered AAPG Rocky Mountain Section I annualmeeting, , MarchI-2, 1951. U. S. Geol.Survey Bull. 491, Veatch,pp.A.239-~242.C" (.1909) Coal deposits¯near Pinedale, Navajo county Arizona. , I i I I I I I I I i I I I I

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